1. Field of the Invention
The present invention relates to portable telephone and other personal communication apparatus and, more particularly, to a protective shield apparatus for absorbing microwave energy to protect a user of the portable telephone and personal communication apparatus from the electromagnetic microwave frequency radiation emanating from such apparatus and to extend the transmission range of such apparatus by redirecting the microwave radiation away from the user of the apparatus. The present invention further pertains to a hand-held radio telephone and antenna assembly for the same. More particularly, the present invention further pertains to a radio signal transmitting device having an antenna assembly effective for enhancing and extending the transmission range of a radiation signal emitted by the hand-held radio telephone, and effective for preventing potentially harmful radiation exposure of the user of the hand-held radio telephone. Further, the present invention pertains to an antenna assembly useful for radio frequency transmission and reception for a communication system, such as a PCS communication system or the like.
2. Description of the Prior Art
There have been a number of contemporary inquires regarding the safety of portable telephones and, more particularly, cellular telephones and wireless communication devices, with respect to the potential danger to the user from electromagnetic microwave radiation associated with the transmission of the signals from such apparatus. When using a hand-held cellular telephone, the user holds the phone with his hand and places the phone to his head so that his ear is in contact with the ear piece of the telephone, and his mouth is at a location close to the mouthpiece of the telephone. This positions the antenna, which usually extends from the top surface of the telephone and/or is disposed on the inside of the telephone case, is in close proximity with the biological tissue of the user's hand and head as it transmits electromagnetic radiation. It has been determined that the presence of the biological tissue alters the radiation pattern and reduces the antenna gain, and, that between 48 and 68% of the power delivered to the antenna of a hand-held cellular telephone is absorbed by the head and hand of the user (see, EM Interaction of Handset Antennas and a Human in Personal Communications, Proceedings of the IEEE, Vol. 83, No. 1, January 1995).
The power absorbed by the head and hand reduces the strength of the radiation signal emitted from the antenna for communication. In addition, by requiring the antenna to output a stronger signal, the power absorbed by the head and hand decreases the usable life of the battery of the cellular telephone.
Further, contemporary inquiries are investigating the possibilities that the radiation absorbed by the head and hand may cause cancer or create other health risks or hazards to the user in association with the use of such apparatus. Research is only now being done looking into the potential link between cellular telephone use and detrimental biological effects, such as brain tumors. However, epidemiological studies have suggested that a link exists between exposure to power frequency electric and magnetic fields and certain types of cancer, primarily leukemia and brain cancer (see, Questions and Answers About Electric and Magnetic Fields Associated With the Use of Electric Power, National Institute of Environmental Health Sciences, U.S. Department of Energy, November 1994). It is clear that consumers will demand protection from hand-held cellular phone radiation as more and more evidence is discovered linking cellular telephone use with potential health hazards.
In response to the anticipated consumer demand, and to provide protection against health risks, the apparatus of the present invention utilizes electromagnetic radiation absorbing materials disposed about the antenna of a portable wireless transmitting apparatus to shield or protect the user from the potentially harmful radiation emissions from the wireless communication apparatus. In addition, to provide enhanced cellular telephone communications, the present invention extends the transmission range of such apparatus by redirecting the microwave radiation away from the user of the apparatus.
Typically, the broadcast from the portable telephones and wireless communication apparatus emit electromagnetic radiation in the microwave frequency range. An example of a prior art radiation shielding apparatus for a radio transmitting device is disclosed in U.S. Pat. No. 5,335,366, issued to Daniels. The shield apparatus of the present invention is disposed primarily about the antenna and transmitting apparatus, both inside and outside of the portable telephone and wireless communication apparatus itself.
A conventional cellular telephone communicates over hard wire phone lines by transmitting electromagnetic radiation signals between the mobile cellular telephone and stationary, ground-based transmission/reception units known as "cells". These cells are typically connected with a hard-wired telephone network, usually through a direct mechanical link. Thus, a user of a cellular phone is not confined by the traditional limitations of being mechanically linked with the hard-wired telephone network. Rather, the user of a cellular phone has mobility due to the radio transmission of the electromagnetic wave signals between the cellular phone and the cells, and is able to communicate via the hard-wired telephone network as long as the cellular phone is within range of a transmission/reception cell site.
The transmission from the portable cellular telephone is traditionally accomplished through an antenna. In a typical hand-held radio telephone, radio frequency transmitting/receiving circuitry is disposed in the interior and a transmitting/receiving antenna is disposed on the outside and/or in the interior of a single compact unit. This type of cellular phone has steadily increased in popularity because of the convenience and mobility afforded by its compact structure. Traditionally, these cellular phones transmit at a cellular frequency range between 800 and 900 megahertz and at a power any where from less than one to six or more watts.
FIG. 32 shows a typical configuration for a hand-held cellular phone, commonly known as a "flip phone". This conventional cellular phone has a main phone body 1 having an ear piece 2 disposed thereon. A mouthpiece 3 is flipped downward in an open position so that when the hand-held cellular phone is appropriately positioned by a user, the ear piece 2 is adjacent to the user's ear, while the mouthpiece 3 is adjacent to the user's mouth. An antenna 4, which may be telescoping or fixed, is disposed externally on the phone body 1. The antenna 4, which may include an antenna disposed inside the telephone case, emits electromagnetic radiation to send communication signals from the hand-held cellular phone to a distant ground-based cell of a cellular network, and receives electromagnetic radiation carrying communication signals from the cell. Thus, the user is able to communicate through the cellular network to the hard wire telephone network, or other receivers via radio signals transmitted from the cell.
However, the antenna 4 of a conventional hand-held radio telephone emits a radiation signal that exposes the user to the health risks now being associated with exposure to electromagnetic radiation in the cellular frequency band. At the present time the exact cause or extent of the health risks are not known, but, it is apparent that there is great demand for a means to shield the users of hand-held cellular phones from unwanted, and possibly harmful, exposure to the radiation generated by the cellular phone. Recent tests have shown that radio waves in and around the cellular frequency band can damage the blood-brain barrier, which protects the brain from toxins. Furthermore, radio frequencies, including the European cellular frequency, have been shown to damage the calcium coating in cells that regulate the passage of hormonal "messages" between cells. Some scientists believe that the brain tissue absorbs some of the power of the electromagnetic radiation. The exact empirical health risks which can be directly linked to the cellular phone are still not known. However, it is apparent that the users and future purchasers of cellular phones are demanding a means to protect themselves as much as possible from exposure to the radiation generated by the cellular phone.
Antenna configurations include the familiar wandlike monopole, which extends from the top of the telephone, interior antennas, which are disposed within the telephone case, and flush mounted antennas, which are usually located on the sides, back or top of the telephone. Each of these antenna configurations suffers from the problems of power being absorbed by the head and hand of the user. In particular, the flush mounted antennas suffer from a higher degree of electromagnetic interaction, since the head and hand are typically disposed very close to the antenna during use of the telephone. Also, the hand holding the telephone tends to mask the flush mounted antenna, causing a detuning effect on the antenna resonant frequency and impedance. This detuning can reduce the communication range of the telephone (see, EM Interaction of Handset Antennas and a Human in Personal Communications, Proceedings of the IEEE, Vol. 83, No. 1, January 1995).
The currently used ground-based cell sites have a number of serious disadvantages. The user of a cellular phone must be within the transmission/reception range of a ground-based cell site for the cellular phone to function. The transmission/reception range between a cellular phone and a ground-based cell site is severely limited by the existence of mountains, buildings or other structures disposed between the ground-based cell site and the cellular phone. Therefore, in places where there are tall buildings, mountains or other obscuring structures it is necessary to maintain a large number ground-based cell sites. Also, there are many locations where it is not practical or possible to maintain a cell site, such as off-shore or sparsely populated locations. Thus, compared to the vast expanses of the Earth, there are currently very few places where a cellular telephone has any use.
To overcome the problems associated with ground-based cell sites, a new means of communication is on the technological horizon of the wireless communications industry. Satellites orbiting the Earth can be used as a means for communication between ground-based locations. The use of orbiting satellites as a communications link has a number of distinct advantages over the use of ground-based cell sites. For example, since the satellites are located high overhead, there is much less chance of a signal being obstructed by a land or building feature, allowing for clearer, more consistent communication. Also, a network of relatively few orbiting satellites can provide communication over the entire surface of the Earth. Thus, satellites can enable communication from remote locations, such as mid-ocean and mountain tops, where it is impractical or impossible to build and maintain cell sites. Also, an expensive to erect and to maintain infrastructure comprising numerous ground-based cell sites is not necessary, thereby allowing developing countries to have the advantages of a communications systems without requiring the investment in numerous expensive components. Conventionally, the use of satellites for communication has required expensive and awkward equipment, typically having a relative large antenna assembly for transmission and reception of a radiation signal. However, there are currently being developed satellite communication systems that will enable communication between small hand-held radio units. A technological problem to be addressed is the design of an antenna assembly that has the transmission range necessary for effective use of an orbiting satellite, while having low power consumption and compact size. The present invention has been devised to overcome the drawbacks of the conventional art and provides a hand-held radio telephone capable of preventing unwanted exposure of the user to radiation, and having and enhanced and extended transmission signal.
Personal communication services (PCS) have recently been introduced to provide communication coverage in locations where a cellular telephone system is impractical to be used. A PCS systems enables communication using a mobile unit in locations such as shopping malls, underground train platforms, office buildings and cities with tall buildings. A typical PCS system is comprised of a number of distributed array antennas that transmit and receive radio signals necessary for communication. However, the capacity of a typical PCS system can be over capacitated when more users wish to use the system then the radio frequency allocated for the system allows.
A conventional radio signal transmitting device, such as a cellular telephone of PCS telephone typically utilize a monopole antenna design. A monopole antenna provides an omni-directional radiation pattern, transmitting the radio signal more or less equally in all directions. However, the use of an antenna that produces an omni-directional antenna pattern has now been shown to have deleterious effects, due to the absorption of the radiation emitted by the antenna by the body, particularly, the head, of the user.
The radio signals transmitted between a radio signal transmitting device, such as a cellular telephone or PCS telephone, can be either digital or analog. Digital radio signals have advantages over analog, such as increased bandwidth capacity and the ability to scramble the digital signal making it a much more private vehicle for carrying data and voice communication. Because of the advantages of digital transmission, PCS operators are opting for its use in their newly developing systems. Further, many cellular telephone carriers are converting from analog to digital technology as well.
Recently, the use of a digital radio signal for the wireless transmission of data and voice has been shown to present serious problems, impacting on the practical use of the digital signal for communication purposes. For example, the digital radio signal transmitted by a radio signal transmitting device, such as a cellular or PCS telephone, is known to interfere with the use of a hearing aid by the hearing impaired. It may also be possible that the radio signal emitted by a radio signal transmitting device will interfere with other electronic devices located on or within the body of the user, such as pacemakers and the like.
There are growing concerns at the Federal Communications Commission and in Congress about the hearing aid interference issue. Members of the wireless telecommunications industry have pledged to develop solutions to the hearing aid interference problem so that the hearing impaired can enjoy the benefits of digital wireless technology (see, RCR, Volume 14, Number 20, Oct. 23, 1995). Thus, there is a recognized need, by both government and industry, to provide a means for preventing the radio signal emitted by a radio signal transmitting device from interfering with other devices. In particular, there is a recognized need to prevent interference with the operation of a hearing aid due to the transmission of a digital radio signal from a radio signal transmitting device.